1. Field of the Invention
The present invention relates to carbon and polymer fibers and, more specifically, to spun fibers that include carbon nanotubes.
2. Description of the Related Art
Carbon fibers are used in many applications, from aircraft structural components to tennis rackets, that require light weight and high strength. Most carbon fibers produced today are made from polyacrylonitrile (PAN) precursor fibers that have been stabilized and then carbonized.
PAN is a synthetic, semi-crystalline organic polymer resin, with the linear formula (C3H3N)n. Most polyacrylonitrile resins are copolymers that include monomers with acrylonitrile as the main component. PAN is often spun into fibers, through a solution spinning process, into a precursor of high-quality carbon fiber. In fact, PAN is used as the precursor for 90% of carbon fiber production.
In one example of the spinning process, PAN powder is dissolved into an organic solvent to form a solution. The solution is spun out through orifices in a spinneret and the resulting fibers are drawn out into an environment in which they solidify as fibers.
To be used in many carbon fiber applications, the fibers must be carbonized in a process that removes non-carbon elements from the fibers. Typically, carbonization is done in an inert environment at high heat. However, the heat required to carbonize PAN fibers will usually destroy the fibers before they become carbonized. Therefore, PAN fibers need to be stabilized prior to carbonization. Stabilization is typically done in air.
Stabilization of PAN fibers results in a ladder-like structure. The stabilization process typically involves heating the fibers in a furnace, in an oxygen rich environment. Once stabilized, the fibers are subjected to a high temperature inert environment to remove non-carbon atoms, thereby forming the carbon fiber.
Existing systems typically expose the PAN fibers to heat in an oven. The stabilization process consumes considerable amounts of energy and takes a considerable amount of time—both of which add to the cost of carbon fibers. In general, fabrication of polyacrylonitrile (PAN)-based carbon fibers requires large furnaces to stabilize and carbonize precursor PAN fibers. These fibers typically go through stabilization in air in the temperature range of 180° C. to 350° C. and carbonized in inert environment between 350° C. to 1700° C. Stabilization time typically varies between 1 to 3 hours.
Also, using the oven-based method of stabilization can result in improperly stabilized fibers. Because all of the heat from the oven radiates from outside the fiber to the inside of the fiber, different levels of stabilization can exist across the cross section of the fiber: the outer shell of the fiber can be over stabilized, while the center of the fiber can be under stabilized. This can result in carbon fiber of poor quality.
Also, the electricity usage of commercial and residential buildings accounts for a considerable amount of all electricity used in the United States. If the building set temperature can be decreased in winter by 4° C. and increased in summer also by 4° C., while providing the comfort to the building occupant, then the building heating and cooling energy consumption can be decreased by 10%. This saving corresponds to more than 1% of the total energy consumed in the United State.
Therefore, there is a need for lower energy method for stabilizing PAN fibers that results in evenly stabilized fibers.
There is also a need for a fabric that can generate heat through the application of an electrical current.